VS-2 and VS-4 VideoSwitch

The Visual Database Systems VS-2 and VS-4
VideoSwitchers are designed to
select a single video output from either two (VS-2) or four
(VS-4)
incoming NTSC video sources. The control is via a TTL level output,
typically from the printer port of an IMB PC or compatible. All input
lines are terminated internally with 75 ohms and the VS-2 &
VS-4 are designed to drive a 75 ohm line output.